Conventionally, mattress innerspring structures comprise a plurality of coil springs or coils which are positioned adjacent one another to extend between top and bottom face surfaces of a mattress. The coils are usually arranged in rows which determine the length and width of the innerspring structure. When individual coil springs or coils are used, they are held together by various means to form a unitary innerspring structure. Alternatively, a row of coils may be formed from a single continuous piece of wire wherein each of the single coils are connected in the row by interconnecting segments. The rows are then fixed together to form the innerspring structure. Examples of such spring assemblies having rows formed of a continuous piece of wire are disclosed in U.S. Pat. Nos. 4,358,097, 4,488,712 and 3,911,511, which are commonly owned with the present application.
The coils in the innerspring structure are typically formed very similar to each other, having generally the same coil diameter and similar stiffness, as dictated by the gauge of wire used to make the coils and the number of turns or pitch of each coil. Therefore, the top surface of a typical mattress will have generally equal firmness throughout the length and width of the mattress made from such an innerspring structure.
However, it is often desirable to make certain areas on the mattress more firm than other areas of the mattress. For example, it may be desirable to firm up the center section of the mattress which receives a majority of the weight from a person lying thereon. Further, it may be desirable to make the edge of a mattress more firm or durable to withstand pressures created when a person sits on the end of their bed.
Varying the stiffness of individual coils, such as by using different wire gauges and/or different numbers of coil turns, it might be possible to change the firmness in certain areas of an innerspring. However, as may be appreciated, such an undertaking would require constant conversion of the coil forming machine, and thus would result in a substantial cost increase attributable to both labor for the machine conversion and the delay in forming the innerspring structures. Furthermore, the availability of various different wire materials and gauges for forming different coils for a single innerspring structure would have to be coordinated. Therefore, such an approach is impractical from a cost standpoint.
It is also desirable to vary the firmness in certain areas of an innerspring structure which utilizes continuous coil spring units. Such continuous coil spring products have met with considerable commercial success, primarily because considerably less material is required for the same degree of firmness in such a spring product than has been employed in spring assemblies which utilize rows of interconnected individual coil springs. However, the spring products made from these continuous coil springs have been found to be difficult or very expensive to modify in order to obtain sections of the product which are more firm than other sections of the same spring product. Varying the wire gauge or coil turns of a particular coil or coils in the product is not a practical option, because all coils are formed of a continuous piece of wire. Furthermore, breaking a particular continuous row of coils into discontinuous sections would destroy many of the benefits of the continuous coil spring product.
Solutions to the aforementioned problems are disclosed in U.S. Pat. Nos. 5,509,642 and 5,803,440, in the form of reinforced coaxial coil units joined together within an innerspring structure to reinforce certain areas in the innerspring. Such a structure may be utilized with individual coils or continuous coil units wherein the coils are formed from a continuous strand of wire.
It is one objective of the present invention to improve upon the existing technology as described above.
To that end, it is another objective of the present invention to make such improvements in the manufacturing of innerspring structures utilizing reinforced coil units.
it is also an objective of the present invention to increase the firmness in selected areas of a mattress, and to increase the durability of selected areas on a mattress which receive a high amount of loading during normal usage.
Furthermore, it is an objective of the invention to provide an innerspring structure at a relatively low cost and with a relatively uncomplicated design.
It is still another objective to provide a continuous coil innerspring product and a method for constructing same which will not require substantial variations in the assembly process in order to form sections of the product with varying firmness.
The above and other objects and advantages of the present invention shall be made apparent from the accompanying drawings and the description thereof.